Sex-links are cross-bred chickens whose color at hatching is differentiated by sex, thus making chick sexing an easier process. Sex-links come in many varieties, few of which are a true breed. As hybrids of laying or dual-purpose breeds infused with extra vigor via heterosis, sex-links can be extremely good egg-layers which often produce 300 eggs a year or more.

Two common varieties are the Black sex-link (also called Black Stars) and the Red sex-link (also called Red Stars). Blacks are a cross between a Rhode Island Red or New Hampshire rooster and a Barred Rock hen. The Black Rock, is another name for a black sex-link. Red sex-links are a cross between a Rhode Island Red or New Hampshire rooster and a White Rock, Silver Laced Wyandotte, Rhode Island White or Delaware hen. In Europe, the Cream Legbar (an actual true-breeding pure breed) and ISA Brown sex-links also exist.

Sex-links are a good choice for ensuring you receive only female hens if your town or city has a law against roosters. Generally sex-links are considered to be a friendly breed

I've found in mine that their prime is their first two years, then they start to slack off in the egg producing. I get a few more every year at TSC. They're egg machines for a while, but all birds have a set amount of eggs in them, so it's gotta stop at some point

You must breed a roo with gold genes ( RIR, HHR, BUff, Partridge, etc...) to hens that has silver genes ( RIWhites, Delawares, SLWyans, etc. are the best ones to use, most White leghorns and some White Rock don't have the silver genes so they wouldn't work. This cross results in chicks that can be sexed by color at hatching, males are white, females are red. Here is a thread with beautiful Golden Comet hens and a GC roo. https://www.backyardchickens.com/forum/viewtopic.php?id=272809

With the Black Sexlinks, You can use any colored rooster as long as he is notBarred and not dominant white (ex.White Lehorn)or masking barring under the white( White Rocks). But any Red, Buff, Black, Blue, Splash, Partridge, Laced, ect roo will work though hatcheries use Production Reds mostly. This cross with give roos that have a white spot on their head and will be Barred and the hens will be solid black was chicks and will be a solid color with maybe red coloring in the breasts as adults.

Here are some sexlinks that I bred from a Buff Orp. roo on Barred Rock hens.